Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.89   10.607%   $204.5013   $204.50   $204.50   $204.50  
  Purchase #2 $240.77   7.862%   $259.6993   $259.70   $259.70   $259.70  
  Purchase #3 $77.87   5.205%   $81.9231   $81.92   $81.90   $81.90  
  Purchase #4 $27.41   8.495%   $29.7385   $29.74   $29.75   $29.70  
  Purchase #5 $66.55   11.680%   $74.323   $74.32   $74.30   $74.30  
  Purchase #6 $31.27   8.577%   $33.952   $33.95   $33.95   $34.00  
  Purchase #7 $181.69   9.149%   $198.3128   $198.31   $198.30   $198.30  
  7 purchase totals = $810.45       $882.4500   $882.44   $882.40   $882.40